Densimeter



April 21, 1953 F. M. POLE Em 2,635,462

DENSIMETER Filed sept. 2, 1947 2 SHEETS-SHEET 1 FIGB.

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` DENSIMETER Filed Sept. 2, 1947 2 SHEETS-SHEET 2 I H MM @www Patented Apr. 2l, 1953 DENSIMETER Foster M. Poole and Le Roy C. Paslay, University Park, and John F. Gaumer, Dallas, Tex.; said Paslay and said Gaumer assignors to said Poole Application September 2, 1947, Serial No. 7 71,578

16 Claims. l

This invention relates to a densimeter and more particularly to a densimeter for measuring the densities of iluids.

Among the several objects of the invention may be noted the provision of a densimeter for accurately and continuously indicating the densities of iiuids, both liquid and gaseous; the provision of a density meter which at all values of fluid densities will automatically compensate for temperature-induced density variations in a iluid being tested; the provision of a densimeter of this class which is adaptable to density indicating and control purposes; and, the provision of a densimeter of the class described which is dependable in operation and of reliable construction. Other objects Will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts which will be exemplied in the structures and methods hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

Fig. 1 is a side elevation of a vibratory element of the present invention with its casing shown in section;

Fig. 2 is a vertical section taken on line 2-2 of Fig. l, the top portion of the casing being broken away,

. Fig. 3 is a horizontal section taken on llne 3-3 of Fig. 2; and,

Fig. 4 is a circuit diagram.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

The present invention utilizes the principle that the natural resonant frequency of any Vibratory element or system may be varied by a change in its mass. Thus, in accordance with the present invention the variation in frequency of a vibratory element or system is used to indicate density variations of fluids which are internally contained in such a vibratory element or system.

Referring now more particularly to Figs. 1 to 3, there is shown at numeral I a vibratory element or system. This vibratory element l includes two hollow tines 3 and 5 which are rmly aixed vby brazing or a like method in a iixed base block 24. These tines have their walls thinned out at 28 so as to favor vibratory movements. The tine 3 is provided with a. bottom 6 which by means of a connector I and adaptor 9 is connected to an inlet conduit Il. An adaptor I3 and an inlet fitting l5 are utilized to extend the passage of conduit il through a cup-shaped supporting base l1.

Tine 5 is similarly provided with a bottom cap I8, a connector I9, an adaptor 2l, a conduit 23, an adaptor 25 and an outlet iitting 2'1. Tines 3 and 5 are supported by and extend through the block 24 which by means of a bracket 29 and bolts 3| is rigidly aiiixed to the base I1. Block 24 is provided with an internal passage to permit communication between the interior of tine 3 and the interior of tine 5. Suitable drain plugs 33 and 5I permit access for cleaning purposes.

Tine 3 contains a tube 35 having perforations 31 at its upper end and having a machined disc 39 rigidly aflixed and sealed to its upper end. The lower end of tubing 35 is snugly but removably iitted into the bottom cap '5, to provide easy removal for cleaning purposes. The upper and lower surfaces of the disc 39 are sealed against the top edge of tine 3 by means of threaded cap 4l.

Tine 5 is similarly provided with a tube 43 having perforations 45 and a disc 41 at its upper end. Aremovable cap 49 is similarly provided for tine 5. Caps 4l and 49 have afxed to their upper surfaces bolts 53. These bolts together with adjustment nuts are utilized exactly to match the vibratory characteristics of tines 3 and 5.

An electromagnetic vibrating driver 51 is mounted on a bracket 5S and is positioned so as to act upon two magnetic shoes 59 which are mounted respectively upon tines 3 and 5. Microphones 6| and B3 are respectively supported by bracket 58 in juxtaposition to tines 3 and 5, respectively. The electrical output from the microphones Si and 63 is conducted by means of wires 65 carried by a cable 61 which passes through the cup-shaped base IT. The electrical input to the electromagnetic driver 5'! is carried by wires E9 of said cable 61. The entire assembly of the vibratory element l and its corresponding -components are sealed by means of a casing 1I. The cup-shaped base Il may be mounted conveniently by means of a bracket T2.

Referring now more particularly to Fig. 4, a pipe line adapted to conduct fluid, is shown at reference numeral 13. A pipe l5 interconnects pipe line 13 with a pump 11, a constant temperature auxiliary heater T9, which may be omitted if desired, and tine 3 of vibratory element I. A pipe 8| connects the tine 5 to a temperature compensating unit 83. An outlet pipe 85 provides for iiuid communication between the temperature compensator unit 83 and the pipe line 13.

The microphones 6| and 53, which are preferably of the pick-up coil type, are connected through a wire t1, a wire 89 and a condenser Sl to the input of a vibrator electronic drive unit I. These wires 81, 89 and condenser 9| supply the grid circuit of a vacuum tube ill. The circuit components of the tube lt include a cathode resistor l, a screen resistor |02, a screen bypass condenser |93, a plate load resistor itil, a plate by-pass condenser |05, and a plate isolating resistor it. The output of the tube itt is transmitted through a coupling condenser |31 to the control grid of an amplifier tube m9. The circuit of the amplier tube |69 includes a grid resistor a cathode resistor H3, a decoupling condenser l| and an isolating resistor ||1. One output of tube It@ proceeds to the electromagnetic driver t? through wires llB and l2l.

The other output of tube |69 is through a wire |23 to an automatic volume-control circuit including a diode tube 225, a battery |21 and a condenser i253. A feed-back circuit through a resistor l3l and a wire |33 is provided between the diode |25 and 'the grid return circuit of tube it. The output of tube |39 is transmitted through a coupling condenser E35 to three amplier tubes |31, |38 and lill. The circuit components of tube |31 include a resistor |38, a grid coupling condenser hlt, a cathode resistor |43 and a winding i615 of a three phase transformer lill. rThe circuit components of tube |35 include a potentiometer U5, a cathode resistor |51 and a transformer winding |53. The circuit components of tube lill include a resistor |55, a condenser !51, cathode resistors |58 and |59, and a transformer winding |5l3. A battery itl, or another suitable source of D. C. power, supplies D. C. energy through wires |63 and 65 to the various vacuum tubes and circuit components of the driver unit I. The three-phase output of the transformer lfl is connected through wires A to the stator of a three-phase selsyn motor, |61, shown at the lower left.

rlhe output shaft |69 of the selsyn motor |61 is connected through gears lil and |13 to an indicating device on a shaft |11. Shaft |11 is adapted to drive a set of three variable resistors C-l, C`2 and C-S in the temperature compensator unit 83 in an opposite direction to three similarly driven variable resistors D-i, D-2, and D-3. Variable resistors C-i, C-2, and C-3 are wound with negative resistance coefficient type wire while the inversely driven variable resistors D-l, D-2 and D-S are wound with Zero resistance coefcient type wire. By negative resistance coefficient type wire is meant wire which has its resistance decreased by an increase in temperature (or increased by a decrease in temperature). By zero resistance coeicient type wire is meant Wire which has its resistance substantially unaffected by temperature. A set of three resistors E-l, E-Z and lil-3 are connected in series with C-l and IJ-l, C-Z and D-Z, and 0 3 and D-, respectively. These six variable resistors and the three resistors are all enclosed in the temperature compensator unit 83 having a well containing resistors E-l, E-2 and E`3 immersed in the fluid. A set of three condensers |15, |8 and |33 in combination with the six variable resistors and three resistors of the .temperature compensator unit S3 complete the input network circuit for a phase shift oscillator unit I I through wires |81, |88 and IBS, and a condenser l9l.

The phase shift oscillator unit indicated at numeral II has components equivalent to the corresponding components of the driver unit I described above. Therefore, in the interest of brevity, the components of the phase shift oscillator unit II carry reference numerals corresponding as to the last two digits of the numerals of the respective equivalent components ofmvibratory driver unit I; the reference numerals of unit I, however, are prefaced by l and the reference numerals of unit II being prefaced by 2. The operation, construction and circuits of unit I are respectively identical with those of unit II with the single exception that there is no output taken from the plate of tube 2&9 as is taken from the plate of tube H39; the oscillatory circuit in unit II being completed by a wire |23. Because of this single circuit difference a plate resistor 2 I8 is added to supply a load to the tube 289 which resistor is equivalent to the electromagnetic driver 51 which is the load of tube |59. The three-phase output of the phase shift oscillator unit II is connected to the rotor of the three-phase selsyn motor |51 by means of the wires B.

Operation is as folllovvs: A iiuid, the density which is to be determine is initially caused to flow through pipe line 13. A portion of this fluid is oy-passed through the pipe l5 and through the vibratory element or system l. A relatively constant flow of this fluid is insured by the use of the pump 11. The .duid may be maintained at a relatively constant temperature, if desired, by the use of the constant temperature unit 19. Referring to Figs. 1-3, the fluid is conducted through the conduit l| to the interior of tine 3 to the tube 35. After passing upward in the direction of the arrows through tube 35 the fluid flows downward through the tine 3 and through the central channel of block 24 to the interior of tine 5 where it is conducted upward and through the perforations 55 of tube t3, and then downward in the direction of arrows and out through the conduit 23. The iiuid then is conducted by the pipe 8l, Fig. Ll, to the temperature compensator unit 83 and is returned to the pipe line 13.

Any casual noise or Vibration will cause microphones tl and 53 to produce an electrical signal which will be transmitted through wires 8l and 89 and condenser 9| to the input grid of tube 'ISS of the driver unit I. This signal is amplified by the tu'be lill! and fed through the coupling condenser |01 to the amplifier tube |99. The output of tube |09 through wires H9 and |2| energizes the electromagnetic driver 51 which in turn will actuate the tines 3 and 5 of the vibratory element l. This movement of the tines 3 and 5 will be transformed into another signal being transmitted to the microphones 6| and 53, which will in turn, through the associated circuits of tubes l vand IDS set up an oscillation, the frequency of which is dependent upon the natural resonant frequency of the vibratory system If the density of the fluid flowing through the tines 3 and 5 remains constant this natural resonance frequency will not change.

In order to maintain the level of the signal through the oscillatory circuit at a relatively constant level the tube |25 has been employed. When the peak voltage of the oscillatory signal, as measured at the plate of tube |69, reaches an amplitude which exceeds a potential determined by battery |21, the diode tube |25 starts rectifying, thus impressing a negative bias on tube |00 through wire |33. Tube |00, which may be of the variable mu type, thus has its gain effectively controlled by the action of tube |25. The amplitude level of the oscillatory signal through tubes |00 and |09 is maintained substantially constant to deliver a relatively constant amplitude signal through the coupling condenser |40 to the tubes |39, |31 and |4|.

The arrangement of tubes |31, |39 and |4| is such that the outputs of these three tubes as characterized by the signals in transformer windings |45, |53 and |60, will be 120 out of phase respectively one with the other. Thus the output phase of the signal on the plate of tube |31 lags the output signal on the plate of tube |39 by 60. The phase of the plate signal on tube |4| leads that of the signal on plate of tube |39 by 60. As the direction of windings |45 and |60 are inverse to the direction of winding |53 there will be a 120 phase difference between the outputs of these three windings. The potentiometer |49 provides a means for adjusting the amplitude of the signal of tube |39 so that the amplitudes of the three output phases are at all times equal.

The three-phase output of transformer |41 is fed to the stator of the selsyn motor |61. If the phase and the frequency of the input to the stator of motor |61 is identical with the phase and frequency of the output of transformer 241 to the rotor of selsyn motor |61, there will be no movement of the shaft |69. If, however, the frequency and the phase of the output A of the driver unit I differs from that of the output of the phase shift oscillator unit II, selsyn motor |61 will be energized and will operate until the output of the phase shift oscillator unit II corresponds in frequency and phase to the output of vibratory driver unit I. The phase and the frequency of the output of the phase shift oscillator circuit II is dependent upon the relative settings of the variable resistors C-l, C-2, C3, D-I, D-2 and D-3. Thus upon a movement of shaft |11 by selsyn motor |61 these six variable resistors in the temperature compensator unit 83 are varied and cause a corresponding frequency and phase change in the input signal through wires |81 and |08 and |89 to the input circuit of tube 200. This signal is amplified by means of the tubes 200 and 209 together with their associated circuit components and -by means of the lead |88 a feed-back circuit is established which maintains an oscillatory resonant circuit, the frequency of which is determined by the frequency of the input signal through the wires |81, |09 and |9|. The amplitude level of this oscillatory signal is maintained substantially constant by the action of A. V. C. tube 225, and the three vacuum tubes 231, 239 and 24| provide a threephase output signal across the windings 245, 253 and 260 respectively. The output of the threephase transformer 241 is connected to the rotor of the three phase selsyn motor |61. Movement and the direction of movement of the selsyn motor |01 is therefore dependent upon any frequency and phase differences between the outputs of the vibratory driver unit I and that of the phase shifter oscillator unit II.

' Thus it can be seen that any variation in the resonant frequency of the vibratory element causes a corresponding variation in the output frequency of the driver unit I. This variation in the output of driver unit I will cause a corresponding deflection of the indicating device |15, which is calibrated in absolute density units, and a change in the output frequency of the phase shift oscillator unit II. Under normal operating conditions the output of transformer |41 will be in phase respectively to the corresponding windings of transformer 241 and the frequency output to the rotor and the stator of the selsyn motor |61 will be the same. Only for a short period of time while the selsyn motor is actually in movement will the phase and frequency outputs of unit I be different from that of unit II. Any variation in temperature of the fluid being measured will cause a variation in frequency. To insure a greater accuracy the temperature compensator unit 83 is provided. Variable resistors C-I, C-2 and C-3 are of negative coefficient wire and when the fluid temperature increases the resistance of these resistors will decrease causing a corresponding increase in frequency in the input signal to tube 200.

The density of the fluid flowing through vibratory element will be similarly decreased which will cause a corresponding rise in vibratory frequency. Variable resistors C-I, C-2 and C-3 are so attached to shaft |11 that when the density of the fluid decreases the effective resistance of these resistors is greater which will give a greater amount of temperature compensation. The temperature-induced decrease in density of the uid causes the vibratory frequency of element to increase which causes a decrease in the effective resistance of variable resistors D-l, D-2 and D-3, which resistance decrease is relatively greater per degree of rotation of shaft |11, than the resistance increase of resistors C-I, C-2 and C-3. Thus, the net effect of the temperature compensator unit 83 is to insure that there will be no change in the absolute density reading as indicated by indicating device |15 when the change in density of the fluid is due solely to temperature variation and not to an actual density variation. It should be noted that the tem' perature compensator unit 83 is a network of variable and fixed resistances some of which are of negative coefficient wire. By proper connection of this network an effective non-linear or linear temperature compensation can be obtained. For example, where density is read on an A. P. I. scale, non-linear temperature compensation is desirable.

To calibrate the density meter of the present invention, the vibratory element or system is filled with uid of a known density at a temperature, and by proper manipulation of the adjustment nuts 55 of tines 3 and 5, the indicating device |15 is adjusted to give a density reading equal to that of the known density of the fluid `at that temperature.

It is clear that the density indication at the member |15 may be transmitted to any remote point by known transmitter means. It is also clear that any indication in element |15 of deviation of density from some predetermined norm may be caused to set in motion mechanism for correcting the deviation. For example, if the deiiection from a norm of the indicator |15 is too far in the direction of increased density, suitable means may be set into motion to introduce into the pipe 13 a uid of lower density so as to average down the density of the resulting mixture. Or, if the deection from a norm of the indicator |15 is too far in the direction of decreased density, suitable means may be set into motion to introduce into the pipe' a fluid of higher density so as to average up the density of the resulting mixture. This is possible because of the continuously reading characteristics of the device, including continuous indications of fluctuations. Thus it will be seen that the present invention is useful not only for indicating density conditions, but provides means for initiating corrections of deviations from desired density conditions. An exemplary use would be in the petroleum industry where it is often desired to maintain a fuel oil output at a predetermined specific gravity (density). And whatever vresults are attained are independent of temperature fluctuations, which is of great importance in any application of the invention to practical ends such as outlined. A further example of such control in the petroleum industry is the shutting off of a valve in a pipeline where oil of one density is followed by oil of another density and it is desired to switch the oils into separate tanks.

It is to be understood that under conditions wherein the temperature of the fluid under investigation remains constant, there would be no need for a temperature corrective circuit such as II. In such event the output frequency of the lines A would be a measure of the natural frequency of the mechanical system (including fluid). Under such conditions these lines are to be connected to a frequency meter or the like not shown which when properly calibrated would read directly in terms of the density. Conversely, if the temperature corrective circuit is used, the temperature of the fluid need not be maintained substantially constant.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings vshall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A densimeter for measuring the density of iiuids'comprising a hollow vibratory mechanical system, circulating means for moving iiuid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained 'iiuid at said natural frequency, electric pick-up means responsive to the vibrations of the systemv including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a rst output, a second electronic circuit having a second oscillatory output, and means adapted to indicate said natural vibratory frequency responsive to incipient frequency and phase differences between said first and second outputs to maintain the frequency and -phase of said second output substantially the same as that of said first output.

2. A densimeter for measuring the density of fluids comprising a hollow vibra-tory mcchanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said systemvincluding the contained iiuid at said natural frequency, electric tra pick-up 'means responsive to the vibrations of the system including the iiuid, an -electronic circuit responsive to said pick-up means and adapted to Vproduce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, means responsive to incipient frequency and phase differences between said Vfirst and second outputs to maintain the frequency and phase of said second output substantially the same as that of said first output, and indicating means actuated by said lastmentioned means to move in accordance with frequency variations of said iirst output and thus continuously to indicate the density of said con tained iiuid.

3. A densimeter for measuring the density of fluids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fiuid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, means in said second circuit responsive to the temperature of the fluid adapted to vary the frequency and phase of said second output to compensate for temperatureinduced density variations of said iiuid, and means adapted to indicate said natural vibratory frequency responsive to incipient frequency and phase differences between said first and second outputs to maintain the frequency and phase of said second output substantially the same as that of said first output.

4. A densimeter for measuring the density of fluids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained iiuid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the iiuid, an electronic circuit responsive to said pick-up meansand adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second oscillatory output, means in each of said electronic circuits for maintaining substantially constant the amplitude of the respective outputs, and means adapted to indicate said natural vibratory frequency responsive to incipient frequency and phase differences between said first and second outputs to maintain the frequency and phase of said second output Vsubstantially the same as that of said first output.

5. A densimeter for measuring the density of iiuids Vcomprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, means in said second circuit responsive to the temperature of the fluid adapted to vary the frequency and phase of said second output to compensate for temperature-induced density variations of said fluid, means in each of said electronic circuit for maintaining substantially constant the amplitude of the respective outputs, and means adapted to indicate said natural vibratory frequency responsive to incipient frequency and phase differences between said first and second outputs to maintain the frequency and phase of said second outputs substantially the same as that of said first output.

6. A densimeter for measuring the density ofl fluids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a, unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, means responsive to any incipient differences between the frequencies and phases of said two outputs adapted to move in accordance with said differences but to maintain an assumed position when said frequencies and phases are identical, whereby the density of said contained fluid is continuously indicated.

'7. A densimeter for measuring the density of fluids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, and means fed by said first and second outputs adapted to move only when either the frequencies or phases of said outputs are unequal, the frequency and phase of the second circuit being responsive to the movement of said means, whereby the density of said contained fluid is indicated.

8, A densimeter for measuring the density of fluids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a. natural frequency of vibration, an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric 10 pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a rst output, a second electronic circuit having a second output, means in said second circuit responsive to the temperature of said fluid to compensate for temperature-induced density variations of said fluid, and means fed by said first and second outputs `adapted to move only when either the frequencies or phases of said outputs are unequal, the frequency and phase of the second circuit being responsive to the movement of said means, whereby the density of said contained fluid is indicated.

9. A densimeter for measuring the density of uids comprising a hollow vibratory mechanical system, circulating means for moving fluid through said system, said system including the contained fluid having a natural frequency of vibration, an electric driver for mechanically vibrating as .a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, an electronic circuit responsive to said pick-up means and adapted to produce electrical oscillations in accordance with the mechanical vibrations and to energize said driver, said electronic circuit having a first output, a second electronic circuit having a second output, means in said second circuit responsive to the temperature of said fluid to compensate for temperature-induced density variations of said fluid, electronic means in each of said circuits for maintaining substantially constant the amplitude of the respective outputs, and means fed by said first and second outputs adapted to move only when either the frequencies or phases of said outputs are unequal, the frequency and phase of the second circuit being responsive to the movement of said means, whereby the density of said contained fluid is'indicated.

l0. Apparatus for responding to the density of fluids comprising a hollow vibratory system adapted to contain a fluid the density of which is to be determined, said system including a contained fluid and having with said fluid a natural vibratory frequency of resonance, 'an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of the system including the fluid, a regenerative circuit connected between the pick-up means and the driver and feeding an output, and frequency responsive means connected with said output.

l1. Apparatus for responding to the density of fluids comprising a hollow vibratory system adapted to contain a fluid the density of which is to be determined, said system including a contained fluid and having with said fluid a natural vibratory frequency of resonance, an electric driver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to the vibrations of ther system including the fluid, a regenerative circuit connected between the pick-up means and the driver and feeding an output, means in said circuit for maintaining substantially constant the amplitude of the oscillations therein, and frequency responsive means connected with said output.

12. Apparatus for responding to the density of fluids comprising a hollow vibratory system adapted to contain a uid the density of which is to be determined, said system including a contained fluid and having with said uid a natural vibratory frequency of resonance, an electric driver for mechanically vibrating as a unit said system including the contained fluid iat said natura-l frequency, electric pick-up means responsive to the vibrations of the system including the fluid, a regenerative circuit connected between the pick-up means and the driver and feeding 'a first output, a phase-shift oscillator circuit having a second output, and means connecting said Voutputs responsive to phase and frequency-diiferences between the outputs to move in a direction to cancel said phase and frequency differences.

13. Apparatus for responding to the .density of uids comprising a hollow vibratory system adapted to contain a fluid the density of which is to be determined, said system including a contained fluid and. having with said fluid a natural vibratory frequency of resonance, an electric driver for Ymechanically vibrating as a unit said system including the contained iiuid at said natural frequency, electric pick-up means responsive to the vibrations Vof the system including the fluid, a regenerative circuit connected between the pick-up means and the driver and feeding ra first output, `a phase-shift oscillator circuit feeding a second output and having a temperature-'responsive circuit componentmeans Yconnecting said outputs responsive to phase and frequency differences between the outputs to move in ,a direction to cancel said phase and frequency differences, said temperature-responsive component and the fluid being in heat ei;- `change relationship.

14. Apparatus ifor responding to the density of viiuids comprising a hollow vibratory system adapted to contain a :duid the density of which is to be determined, said .system including a contained fluid .and having with said fluida natural vibratory frequency of resonance, an electric driver for mechanically vibrating as a unit said system including the contained fluid at .said natural frequency, electric pick-up means responsive to the vvilcuati'ons of the system including the fluid, a regenerative circuit connected between 'the vpick-up Ineans and the driver and feeding a first output, a phase-shift oscillator circuit feeding a second output and having .a temperature-responsive circuit component,means connecting said outputs responsive to `phase and frequency differences between the outputs to move in a direction to cancel said phase and frequency differences, said temperature-.responsive component and the fluid being 1in heat exchange relationship, and means in each of said 1.2 circuits for maintaining constant and equal the amplitudes ofthe oscillations therein.

15. Apparatus for 'responding to the density of fluids comprising a hollow vibratory vsystem adapted to contain .a .fluid the density of which is to be determined, said system including Aa contained fluid and having with said fluid a natural vibratory frequency of resonance, .circulating means for moving iiuid through said system, .an electric driver for mechanically vibrating as a unit said system including the contained :uid at saidnatural frequency, electric pick-up means responsive to the vibrations of the system includ- `ing the fluid, a regenerative circuit connected between the pick-up means .and the driver and feeding ran output, and frequency responsive means connected with said output.

16. Apparatus for responding to the `density of uids :comprising a hollow vibratory system adapted to contain a fluid the density of -which iis to be determined, ysaid system including `a contained :duid and having with said fluid fa natural Vvibratory frequency of resonance, an electric ldriver for mechanically vibrating as a unit said system including the contained fluid at said natural frequency, electric pick-up means responsive to `the vibrations of the system 4including the fluid, a regenerative circuit connected between lthe pick-up means and the driver and feeding an output, means in said circuit rfor maintaining substantially constant the amplitude of vthe oscillations therein, frequency responsive means connected with said output, and means responsive 'to the temperature -of said fluid to Vary the yfrequency of said oscillations to compensate 'for ltemperature induced density variations `of said ijuid.

FOSTER M. POOLE.

LE ROY C PASLAY. JOHN F. GAUMER.

References `Cited in .the `.ille of this patent UNITED STATES PATENTS Number Name Date 1,570,781 Ruben Jan. 26, 1926 1,643,668 Lindbald Sept. 27, 1927 1,921,501 Bower` Aug. 8,1933 2,183,399 Heising Dec. '12, 1939 2,283,750 Mikelson vMay 19, 1942 2,306,137 Pabst et al. Dec. 22, 1942 V2,361,396 Gross Oct. 31, 1944 V2,447,098 Silverman Aug. 17, 1948 2,511,137 Wheeler June 13, 1950 FOREIGN PATENTS Number Country 'Date '574,819 Great Britain Jan. 22, 1946 664,763 Germany Sept. 3, 1938 

